Press a cold pack to your forehead and (at least according to one small experiment) you become much harder to make yawn.
That is the finding behind the thermoregulatory theory of yawning, or brain cooling model. It holds that a yawn does more than signal tiredness or boredom, and may serve in part to cool the brain. The first direct evidence came from a 2007 paper by Andrew Gallup and Gordon Gallup, published in the journal Evolutionary Psychology.
The finding is worth taking seriously. It is also one study, from one laboratory, built on a few dozen undergraduates, and it should not be read as the final word on why we yawn.
What the experiment actually did
The Gallups ran two experiments, both using contagious yawning as their measure. In the second, thirty-three students at the University at Albany each held a pack to the forehead while watching video of other people yawning. The packs came at three temperatures: warm at 46 degrees Celsius, cold at 4 degrees, and one at room temperature.
In the warm and room-temperature groups, 41 per cent of participants caught a yawn. In the cold group, that dropped to 9 per cent. So the warming did not make people yawn more. The cooling made them yawn less.
The first experiment pointed the same way through breathing. Participants who were given no breathing instructions, or who were told to breathe through the mouth, caught yawns about 48 per cent of the time. Those instructed to breathe through the nose, which is thought to lower brain temperature, did not catch a single yawn. The authors read both results as cooling the brain and, with it, removing whatever normally triggers a yawn.
Why they measured a caught yawn rather than a spontaneous one
This is the part most quick summaries skip. The experiments did not measure ordinary yawning. They measured contagious yawning, the reflex to yawn when you see someone else do it.
The reasoning in the paper is that a caught yawn is difficult to tell apart from a spontaneous one once it starts, and it can be switched on reliably in a lab by showing a video. That makes it convenient to study. It also means the whole result rests on treating the caught yawn as a stand-in for the real thing, which is a reasonable assumption rather than a demonstrated fact. If the two turn out to work differently, the forehead result would need rereading.
One laboratory, a widening case
The 2007 study did not stay alone. Over the following years the same research line extended the temperature logic across species, reporting that yawn frequency tracked ambient temperature in budgerigars and in rats. In humans, a 2019 study moved the cold pack from the forehead to the neck, applying warm, cold and room-temperature packs over the carotid arteries and again finding that cooling lowered contagious yawning. Thermal imaging was used to confirm the packs shifted temperature near a region used as a proxy for brain temperature.
By early 2013 the argument had been gathered into a review, summarising more than five years of work in Frontiers in Neuroscience. Taken together, the studies are more than a single curiosity. They are a sustained line of argument. What they are not is a broad consensus, because a large share of the work traces back to the same small circle of researchers.
What the theory still cannot settle
Sample sizes here are small.
That forehead experiment split thirty-three people into three groups, which is enough for a statistically significant drop in the cold condition but not enough to close a question that has run for decades.
There is also a rival tradition. The late Robert Provine, who spent much of his career on yawning, treated it mainly as a marker of shifts in arousal and internal state, and treated the contagious version as something closer to social and empathic mimicry than to temperature control. The two views are not flatly incompatible. A yawn could regulate state and cool tissue and spread through a group. But the cooling model has not displaced the alternatives, and reviewers in the field still describe the ultimate function of yawning as unresolved.
Cooling the head lowered how often people caught a yawn, in the direction the brain cooling theory predicts. That much is consistent with the theory. Consistent is not the same as proven, and the result does not rule out that yawning does several things at once.
What would move the argument is replication at larger scale, by laboratories with no stake in the theory, and a clearer account of whether spontaneous and contagious yawns share the same machinery. Until then the cold pack remains a genuine and repeatable effect in search of a settled explanation.
